JAC Advance Access published online on May 4, 2007
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm126
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A highly carbapenem-resistant Pseudomonas aeruginosa isolate with a novel blaVIM-4/blaP1b integron overexpresses two efflux pumps and lacks OprD
1 Department of Microbiology, Medical School, University of Thessaly, Larissa, Greece 2 Department of Obstetrics and Gynaecology, Medical School, University of Thessaly, Larissa, Greece
Received 15 December 2006; returned 1 March 2007; revised 13 March 2007; accepted 8 April 2007
* Correspondence address. Department of Medical Microbiology, University Hospital of Larissa, Mezourlo, 411 10 Larissa, Greece. Tel: +30-6976-881203; Fax: +30-2410-681570; E-mail: pournaras{at}med.uth.gr
Objectives: A Pseudomonas aeruginosa clinical isolate that exhibited high-level carbapenem resistance and produced metallo-ß-lactamase (MBL) was recovered from a Greek patient. This study was conducted to determine the underlying mechanisms that conferred the carbapenem resistance phenotype.
Methods: MICs were determined by Etest and Etest MBL. PCR assays were performed for identification of blaVIM-type, other antibiotic resistance and efflux pump genes and mapping of class 1 integrons. Expression of efflux pump genes was quantified by real-time PCR. Nucleotide sequencing was used to determine the blaVIM allele. The location of the MBL allele was investigated by mating experiments, plasmid analysis and hybridization studies.
Results: The isolate was highly carbapenem-resistant (MICs of imipenem and meropenem were 512 and 128 mg/L, respectively) and multidrug-resistant. It harboured the ß-lactamase genes blaVIM-4 and blaP1b in a novel class 1 integron named InV4P1, and a second integron with aac(6’)-Ib and blaOXA-35 gene cassettes. The isolate was deficient in porin OprD and overexpressed efflux pumps MexAB-OprM and MexXY-OprM. Conjugation experiments failed to detect transferable MBL determinants, plasmids were not visualized and blaVIM was detected by PCR in the chromosomal band.
Conclusions: Multiple carbapenem resistance mechanisms are demonstrated to coexist in a single P. aeruginosa isolate and might confer the high-level carbapenem resistance.
Key Words: PSE-1 , InV4P1 , P. aeruginosa
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